Spectroscopy and ESCA

Techniques that enable the observation of specific valencies of cations include E.S.R., 7-resonance spectroscopy and ESCA, and have been considerably improved in the recent years. 

Before the advent of ultraviolet photoelectron spectroscopy and ESCA, experimental evidence on the energy density was mainly available from static magnetic susceptibility and specific heat measurements (134). These provide information on the density of states at the Fermi level and it is impossible to base any conclusions on such experimental information with regard to the shapes of the d-bands in the alloys. It is currently believed that there is very little transfer of d-electrons between the atoms. If an increase in the number of d-electrons on a particular atom does occur, it is due to transfer of electrons from the s,p-band to the lower d-band. This is, of course, related to the difference in electronegativity of the alloying components (135a, 135b). 

Electron beam techniques have aided electrical measurements greatly, but these methods often lack sensitivity (X-ray and Auger spectroscopy and ESCA [electron spectroscopy for chemical analysis]) and accuracy (SIMS [secondary-ion mass spectrometry], etc.), two attributes that are of prime importance in IC process technology. Fortunately, materials can be analyzed with both accuracy and sensitivity by wet chemical analysis. 

For a recent review on a critical evaluation on classical methods see Fardim et al. [123]. In addition to the wet chemical methods, FTIR spectroscopy and ESCA [124,125] techniques have been applied to quantify carboxyl groups in cellulose and pulp. In case of FTIR, satisfactory results in comparison to wet chemical analysis could only be obtained with carboxyl-rich samples [ 126— 128],... 

Lunsford and coworkers (26) have prepared a Ru(bpy)32 complex in zeolite Y and studied the quenching of oxygen and water. The emission bands of the ion-exchanged zeolite resemble those of aqueous solutions. Diffuse reflectance spectroscopy and ESCA measurements were also made in the characterization of these samples. 

Since the presentation of this paper additional experimental Information on transition metal carbides indicates that the peak shift of the Ti Lm band should be interpreted differently than was done in the present paper. Recent experimental results by soft x-ray spectroscopy and ESCA (electron spectroscopy by chemical analysis) indicate that if there is ionic character in TiC, electrons are being transferred from titanium to carbon. A complete discussion of this is in print [24]. 

In an examination of the literature dealing with the study of non-aqueous solutions, it is striking that there is virtually no experimental procedure for the investigation of matter that has not been employed to study solvation or other processes involving solvent effects. Scarcely does a new method appear in the arsenal of the analyst than it is applied to this field of solution chemistry. This tendency is well shown by the example of typical methods, developed for the investigation of solid substances, such as Mossbauer spectroscopy and ESCA. The application of these to the study of solvation processes was made possible by the elaboration of the technique of quenching solutions by rapid freezing. 

The mechanical properties of the composite sheets made in laboratory are tested according to ASTM methods. The impact strength, however, was measured at -20 C using Charpy impact tester. All these test results simulate the properties of end product. Besides physical and mechanical properties the chemical characteristics of modified and unmodified composites can be very well correlated from Infrared spectroscopy and ESCA analyses data. 

Surface composition and morphology of copolymeric systems and blends are usually studied by contact angle (wettability) and surface tension measurements and more recently by x-ray photoelectron spectroscopy (XPS or ESCA). Other techniques that are also used include surface sensitive FT-IR (e.g., Attenuated Total Reflectance, ATR, and Diffuse Reflectance, DR) and EDAX. Due to the nature of each of these techniques, they provide information on varying surface thicknesses, ranging from 5 to 50 A (contact angle and ESCA) to 20,000-30,000 A (ATR-IR and EDAX). Therefore, they can be used together to complement each other in studying the depth profiles of polymer surfaces. 

After a few minutes irradiation with a high pressure mercury lamp at about 50 C, a rather complete cover of grafted acrylic acid, acrylamide and other vinyl monomers could be obtained. In later experiments a continuous grafting method has been developed where a tape or a fiber bundle after suitable pretreatment is grafted by UV irradiation for a few seconds. Homopolymer formed is removed by washing and grafted polymer analyzed by dye absorption, IR reflection and ESCA spectroscopy. 

Membrane morphology is studied with scanning electron microscopy (SEM) thereby providing an Insight into the relationship between asymmetric membrane preparation, structure, and performance (29,3A). The extent of ion exchange of the salt form of the SPSF membranes is studied with atomic absorption spectroscopy (AAS), neutron activation analysis (NAA), and ESCA. AAS is used for solution analysis, NAA for the bulk membrane analysis, and ESCA for the surface analysis. 

A very common and useful approach to studying the plasma polymerization process is the careful characterization of the polymer films produced. A specific property of the films is then measured as a function of one or more of the plasma parameters and mechanistic explanations are then derived from such a study. Some of the properties of plasma-polymerized thin films which have been measured include electrical conductivity, tunneling phenomena and photoconductivity, capacitance, optical constants, structure (IR absorption and ESCA), surface tension, free radical density (ESR), surface topography and reverse osmosis characteristics. So far relatively few of these measurements were made with the objective of determining mechanisms of plasma polymerization. The motivation in most instances was a specific application of the thin films. Considerable emphasis on correlations between mass spectroscopy in polymerizing plasmas and ESCA on polymer films with plasma polymerization mechanisms will be given later in this chapter based on recent work done in this laboratory. 

Several factors have contributed to this goal in the recent past development of electrochemical techniques for the study of complex reactions at solid electrodes, use of physical methods such as ESCA, Auger, LEED, etc. for the study of surfaces in the ultrahigh vacuum (UHV) environment and in situ techniques under the same conditions as the electrode reaction. Ellipsometry, electroreflectance, Mossbauer, enhanced Raman, infrared, electron spin resonance (ESR) spectroscopies and measurement of surface resistance and local changes of pH at surfaces were incorporated to the study of electrode kinetics. 

If the complex K2(H30)[Pt2(0H)(H20)(ju-S04)4] is synthesized at higher reaction temperatures, violet-colored peroxo complexes such as K2[Pt2(/i Oi-)2(/x-S04)2(H20)2] are formed. The compounds have been verified by electronic spectroscopy and by ESCA, but no structural characterization has been published.1649-1651... 

The structure assignment problem, which offers difficulties similar to those discussed for the alkylation products, was solved by means of mass spectrometry in combination with isotope labeling at position 2 with 15N. ESCA (X-ray photoelectron) spectroscopy and IR spectra are in agreement with the assignment as a 3-oxide.23... 

Auger analysis and ESCA (electron spectroscopy for chemical analysis) of the cleaned wafers showed no contaminants. However, the ammonium hydroxide solution produced a high mobile-ion content in the grown films. 

Along this line, the limitations of the technique used must be recognized. Some measure predominantly bulk properties, e.g., X-ray diffraction and magnetic susceptibility whereas, others are sensitive to surface composition, e.g., adsorption and ESCA. For example, in one reported study only cobalt in tetrahedral coordination was found on a catalyst by diffuse reflection spectroscopy, but magnetic measurements revealed that octahedral cobalt must also be present (10). Thus, it is dangerous to rely on any one method to characterize these catalysts. 

Reoxidation of the sulfided catalyst gave the same state as the original oxidized catalyst by reflectance spectroscopy, IR, and ESCA. 

Photoelectron spectroscopy (ESCA) and thermal evolved gas analysis (EGA) have been applied to characterize sulfur- and nitrogen-containing species in atmospheric particulate matter. Particulate amines and amides previously identified only by ESCA have been detected by EGA, a bulk method, for the first time. EGA and ESCA results suggest the existence of a sulfate similar to ammonium sulfate but with some of the ammonium ions replaced by a charged organic nitrogen complex. 

The tools available for surface composition characterization are electron spectroscopy for chemical analysis (ESCA), Auger spectroscopy (AES), ion scattering spectroscopy (ISS), and secondary ion mass spectroscopy (SIMS). ESCA spectroscopy is used more widely than the others for studying the surface composition and oxidation states of industrial catalysts, and thus its application will be discussed in limited detail. 

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